Screening of insecticides for toxicity to rice hoppers and their predators

Greenhouse studies were conducted at the Directorate of Rice Research, Hyderabad to assess the toxicity of selected insecticides to rice brown planthopper (BPH) Nilaparvata lugens (Stal) and white backed planthopper (WBPH) Sogatella furcifera (Horvath), green leafhopper (GLH) Nephotettix virescens (Distant) and their important predators viz. green mirid bug (GMB) Cyrtorhinus lividipennis (Reuter), brown mirid bug (BMB)
Tytthus parviceps and veliid predator (VP) Microvelia douglasi atrolineata. The results showed that bifenthrin @ 50g a.i. ha-1 was less toxic to BPH the persistent toxicity (PT) being 1371 compared to GLH (PT 2507) and more toxic to BMB (PT 2667 for nymphs, PT 2800 for adults), GMB (PT 2800) and VP (PT 2800) than monocrotophos @ 500 g a.i. ha-1 (PT for BPH 756, WBPH 1913, GLH 1623, BMB nymphs 1652, adults 2016, GMB 1960 and VP 931). Virtakao 40 WG, a combination product containing 20% chlorantraniliprole + 20% thiamethoxam @ 50 g a.i. ha-1 exhibited higher toxicity to BPH (PT 1184), WBPH PT 2914) and GLH (PT 3000) compared to monocrotophos @ 500 g a.i. ha ha-1, but it was highly toxic to all the predators viz., BMB (PT nymphs 2513, adults 2793), GMB (PT 2800) and V.P (PT 2609). Pymetrozine, a new molecule belonging to pyridine azomethines group @ 125 g a.i. ha-1 exhibited higher toxicity to BPH (PT 1950) & WBPH (PT 2411) compared to monocrotophos @ 500g a.i. ha ha-1 but at the same time it was relatively less toxic to natural enemies viz., BMB (PT for nymphs 2303, adults 2737), GMB (PT 1582) Toxicity of insecticides to rice hoppers and predators and VP (PT 649). The implications of using these new products in rice ecosystem based on the present results for ecological safety are discussed.